THE TIME DELAY OF AIR/OXYGEN MIXTURE DELIVERY AFTER THE CHANGE OF SET FIO2: AN IMPROVEMENT OF A NEONATAL MATHEMATICAL MODEL

Abstract

<p>Oxygen therapy is an essential treatment of premature infants suffering from hypoxemia. Normoxemia is maintained by an adjustment of the fraction of oxygen (FiO₂) in the inhaled gas mixture that is set manually or automatically based on peripheral oxygen saturation (SpO₂). Automatic closed-loop systems could be more successful in controlling SpO₂ than traditional manual approaches. Computer models of neonatal oxygen transport have been developed as a tool for design, validation, and comparison of the automatic control algorithms. The aim of this study was to investigate and implement the time delay of oxygen delivery after a change of set FiO₂ during noninvasive ventilation support to enhance an available mathematical model of neonatal oxygen transport. The time delay of oxygen delivery after the change of FiO₂ during the noninvasive nasal Continuous Positive Airway Pressure (nCPAP) ventilation support and during the High Flow High Humidity Nasal Cannula (HFHHNC) ventilation support was experimentally measured using an electromechanical gas blender and a physical model of neonatal lungs. Results show the overall time delay of the change in the oxygen fraction can be divided into the baseline of delay, with a typical time delay 5.5 s for nCPAP and 6.5 s for HFHHNC s, and an exponential rising phase with a time constant about 2–3 s. A delay subsystem was implemented into the mathematical model for a more realistic performance when simulating closed-loop control of oxygenation.</p>